Post on 19-May-2015
Impression materials
by
Bibin bhaskaran
Impression materials
Definition :- (GPT):
1) A negative likeness or copy in reverse of the surface or object.
2) An imprint of the teeth and adjacent structures for use in dentistry
Impression material:- Any substance or combination of
substances used for making an impression or negative reproduction.
Impression technique:- A method and manner used in
making a negative likeness.
inelastic or rigid
elastic
material use material use
Chemical reaction (irreversible)
plaster of Paris Edentulous ridge
Alginate hydrocolloid
Teeth and soft tissues
zinc oxide-eugenol
Interocclusal records
Non aqueous elastomers Polysulfide,polyether Condensation silicone Addition silicones
classification
Thermally induced Physical reaction(reversible)
Compound wax
Preliminary impression
Agar TEETH & SOFT TISSUES
Classification
Based on rigidity : Rigid
eg Plaster,Zincoxide eugenol
impression compound
Elastic
eg Alginate,polyether,silicone
Based on setting of the material: 1.) Chemical reaction(irreversible)
eg plaster of paris,zincoxide eugenol
alginate,additon and condensation silicones
2 ) Physical change of state(reversible)
eg agar
Based on viscosity : Mucostatic
eg impression plaster,agar, light body elastomer
Mucocompressive
eg Impression compound,alginates Pseudoplastic
eg addition silicones
Based on interaction with saliva and water : Hydrophobic eg polysulfide ,condensation silicones Hydrophilic eg putty,impression plasterBased on use : Primary impression material eg impression compound,alginate
Secondary Impression material eg Zoe,medium bodied elastomers Duplicating material eg agar
Based on
Chemical composition : impression plaster
impression compound
metal oxide(zinc oxide eugenol)
pastes
agar hydrocolloid
alginate hydrocolloid
polysulfides
condensation silicones
addition silicones
polythers
light curing polyether
(urethane dimethacrylate)
Desirable qualities
Pleasant odor taste and color Absence of toxic irritants Adequate shelf life Economical Easy to use Setting that meet clinical
requirements Satisfactory consistency
Readily wet oral tissues Elastic Adequate strenght Dimensional stability Compatiblity with cast and die
materials Accuracy Disinfection
Impression plasterADAspecification
Composition
Uses Mixing time
Working time
Setting time
Advantages
Disadvantages
No 25 •Calcined caso4•Anti – expansion agents k2so4•Accelerators k2so4•Retarder borax•Gelatin •Gum tragnath•Starch•Alizarin red
•Primary impression material•Secondary impression material
60 sec Altered by use of additives
same •Good deatail reproduction•Inexpensive •Easy to handle•Non toxic•Increased shelf life•Setting time can be controlled.
•Requires separating medium•Dry sensation to patients mouth
Impression plaster
The impressions are very accurate Being hydrophilic it has got intimate contact with
oral tissues by absorbing surface moisture
Impression compoundADAspecification
Composition
Uses Flow Advantages
Disadvantages
Disinfection
No 3•Type 1-Impression(low fusing)•Type 2-Tray(high fusing)
•Rosin •Copal resin•Carnauba wax•Stearic acid•Talc•Coloring agent
•Type 1-primary impression,peripheral tracing•Type 2-As a tray to support other materials
•Type 1 flow at mouth temp is 6%•Type 2 flow at mouth temp is 2%
•Non toxic and non irritant•Hardens in reasonably acceptable time•Compatible with gypsum products•No separating medium required
•Although plastic not fluid enough to record fine detail•Distorts over undercuts•Shrinkage on cooling•Dimensional change on storage
2%alkaline glutarldehyde
Impression compound
Fusion temperature of impression compound is 43.5 degree celesius
Zinc oxide eugenol impression materialADAspecification
Composition
Uses Mixing time
Setting time
Advantages
Disadvantages
Disinfection
No 16•Type1 (hard)Type 2 (soft)
2 tubesTube 1-•ZnO•Veg or mineral oilTube 2-•Clove oil or eugenol•Gum/polymerised rosin•Filler silica•Lanolin•Accelerators –cacl2,mgcl2
•Impression pastes•Cement•Temporary filling•Root canal filling•Bite registration paste•Temporarly reline material•Surgical dressing
1 min/30-40 sec
Type 1-Initial –3-6minFinal-10 minType 2-Initial-3-6minFinal –15 min
•Adheres well to tray•Sufficiently fluid to record fine detail•No dimensional change in setting process•Hard when set•No separating medium required•Non toxic
•Burning of eugenol•Persistent taste•Adheres to tissue•Rigid material cant be used
2% glutarldehyde
Zincoxide eugenol impression material
Non eugenol pastes-
One of the chief disadvantages of Zoe pastes is the possible burning sensation caused by eugenol.orthoethoxybenzoic acid (EBA) is a valuable substitute for eugenol in this regard.
Alginate ADAspecification
Composition
Uses Mixing time
Working time
Setting time
Advantages
Disadvantages
Disinfection
No 18Type 1(Fast)Type 2(Slow)
•Soluble alginatesNa,K,Ammonia•Calcium sulphate dihydrate•Trisodium phosphate•Diatomaceous earth•Potassium titanium fluoride•Flavourin agent.
•To record impressions of dental arches•Premilinary impression•Duplicating cast and models
Type 1-45secType 2-1min
Type 1-1.25-2minType 2-3-4.5min
Type 1-1-2minType2 –2-4.5min
•Non toxicand non irritant•Acceptable odor•Compatible with gypsum•Elastic •Sufficiently fluid
•Dimensionally unstable•Tears if undercuts severe•Difficult to sterilize•Poor shelf life
•10 min in sodium hypochlorite solution•10 min in iodophor solution •10 min in glutaraldehyde solution
Alginate
Gelation reaction-
2Na3P04 + 3CaSo4----- Ca3(Po4)2+3 Na2SO4
Recent advances in alginates
Dust free alginates-
De-dusting agent (glycerin or glycol)
Siliconized alginates-
silicon polymers are added to strengthen the material
Alginates containing disinfectants-
eg quaternary ammonium salts or chlorohexamine are added to alginate powder.
Hard and soft set alginates-
by adjusting the amount of fillers
Reversible hydrocolloid-AGARADAspecification
Composition
Gelation temperature
Liquefaction temperature
Advantages
Disadvantages
Disinfection
No 11 •Agar•Sulfates (k2so4)•Borax •Alkyl benzoate•Water •Fillers(silica)•Plasticizer(glycerine)•Bactericide (thymol)colors
37 degree celesiusTo45 degree celesius
60 to 70Degree celesius
•No custom tray required•Clean and pleasant•Easy to pour•Inexpensive•Good shelf life•High accuracy•Re-usable
•Requires conditioning unit•Decreased dimensional stability•Weak inn deep sulcus
Iodophor /bleach/glutarldehyde
Agar
Gelation-
Gelation is accomplished by circulating cold water of approximately 18-23 degree for not less than 5 min.
Elastomeric impression materials
Classification :-Based on viscosity-
Class 1 heavy body heavy viscosity
Class 2 regular body or medium body
Class 3 light body or low viscosity
Based on chemistry-
Polysulfides
Condensation silicones
Additional slilicones
Polythers
Visible light curable polyether
POLYSULFIDESADASpecification
Composition
Mixing time
Working time
Setting time
Advantages
Disadvantages
Disinfection
No 19
1,Base paste –•Liquid polymer containing thiol,mercaptan or polysulfide polymer.•Filler –titanium dioxide•Plasticizer-DI-n-butyl phthalate•Sulfur
2,Reactor paste-•Pbo2 or organic hydroperoxides or inorganic hydroxides•Inert oil/plasticizer•Filler -silica •Stearic acid
45 sec-1min
5-7min 8min •No special equipment•Superior strength•Pouring can be delayed to 1 hr•Can be electroplated•Adequate shelf life
•Custom trays required•Hydrophobic•Sensitive to heat•Long setting time•High shrinkage•High permanent deformation
2% glutarldehyde
polysulfides
Polysulfide is one of the least stiff or highly flexible of elastomeric material
For accurate polysulfide impressions- The cast should be poured immediately after taking
impression Minimise the amount of material used to take impression
by using custom made acrylic trays
ADASpecification
Composition
Mixing itime
Working time
Setting time
Advantages
Disadvantages
Disinfection
No 19
2 types- 1,Double mix type 2,Putty type
Base paste-•Polydimethyl siloxane/liquid silicone polymer•Filler –silicaReactor paste-•Tetra functional silicates•Tin compound
45 sec Upto 5 min
10 – 12 min
•No special equipment required•Moderate strenth in deep sulcus•Adequate shelf life•Pleasant odor
•Custom tray required•Difficult to electroplated•hydrophobic
2% glutaldehyde
Condensation silicones(Double mix type)
Condensation silicones
It is also called room temperature vulcanising silicones(RTV)
Uses – It is widely used in recording dentulous impressions in
preparation of crowns,bridges,inlays,onlays and to some extent for partial dentures
It is also used to record edentulous impressions in preparation of complete denture
Putty type
Advantages – No custom tray required No special equipment required Moderate strength in deep sulcus Pleasant odor Adequate shelf life
Disadvantages – Should be poured shortly after removal Hydrophobic Difficult to electroplate Easily distorted
Addition silicones(Double mix type)
ADASpecification
Composition
Mixing itime
Working time
Setting time
Advantages
Disadvantages
No 19
2 types1,Double mix type2, Putty type
•Polymer –polyvinyl siloxane,vinyl polysiloxane,vinyl silicones•Cross linking agent-hydride silicone•Catalyst –chloroplatinic acid
30- 45 sec
Is greater than silicones
10-12min
•No special equipment•Dimensionaly stable•Good shelf life•Pleasant odor
•Custom tray•Hydrophobic •Expensive
Addition silicones
Addition polysilicones are the most stable of all the existing materials
It has an excellent recovery of 99.93% It exhibits pseudoplastic properties.it can be used both
as syringe and tray materials
Putty type
Advantages –
No custom tray No special equipment Good shelf life Can be poured more than once
Disadvantages –
Extremely hydrophilic More difficult to pour Most expensive
Polyether materialsADASpecification
Composition
Mixing itime
Working time
Setting time
Advantages
Disadvantages
No 19Base plate tube-•Pre polymer-ethylene amine•Inert filler-silica•Plasticiser –glycoletherCatalyst paste-•Ester derivatives of aromatic sulphonic acid•Plasticiszer –phthalate•Thinner-octyl phthalate•Methyl cellulose
30-45 sec
2-3min 5-6 min•No special equipment•Finish line easily read•Pleasant odor•Can be poured more than once•Hydrophilic•Good shelf life•Fast setting
•Custom tray•Very stiff•Least tear strength•More expensive
Polythers
Uses- For recording impression in preparation of
crowns and bridges Cavity preparation for inlays and onlays For construction of partial and complete
dentures
Visible light cured polyether
ADASpecification
Composition AdvantagesDisadvantages
No 19Introduced in 1988
Light bodied material=syringeHeavy body=tubes Contains•Polyurethane dimethacrylate resin with sio2 +plasticizer•Polymerises in light
•Complete control over W.T/S.T•Curing time relatively short•Excellent physical/mechanical/clinical properties
•Need for transparent trays•If delay in placement material to be stored in dark place•Difficult to cure remote areas•Should not be used in patients allergic to methacrylates
Light cured polyether
It has excellent elasticity It has infinite working time and short setting
time The impression can be stored upto two weeks
Disinfection
Most manufacturers recommend a specific
disinfectant,such as iodophor,bleach,or glutaldehyde,for disinfection.
Certain disinfectants may result in gypsum casts that have a lower surface hardness or diminished surface detail.
The current protocol for disinfecting hydrocolloid impressions recommended by the centre for disease control is to use house hold bleach(1 to 10 dilutions),iodophor or synthetic phenols as disinfectants
An alternate disinfection method is by immersion,but this should not exceed 10 min.
Duplicating is required for two reasons:-
1, The cast on which the wax pattern of the metal frame work is to be formed must be made from refractory investment because it must withstand the casting temperatures required for gold or base metal alloys
2, The original cast is needed for checking the accuracy of the metal frame work and for processing the denture base portion of the partial denture
The most common duplicating materials are agar hydrocolloid compounds, The primary advantage of agar is their set is reversible.the disadvantage is it is subject to dimensional change.The best storage condition is 100% humidity.
Duplicating materials
Tissue conditoners are soft elastomers used to treat an irritated mucosa supporting a denture.it is used to provide time for healing of soft tissues
Tissue conditioners are composed of powder containing poly(ethyl methacrylate)and a liquid containing an aromatic ester – ethyl alcohol.
The properties that make tissue conditioners effective are-
1,viscous behavior which allows adaptation to irritated denture bearing mucosa
2,viscoelastic behavior which cushions the cyclic forces of mastication and bruxism
Tissue conditioners
Zardiackas.L.D , Dental materials,Dentla clinics of morth america,July 2007,vol 51,pg 629-643 .
O’Brien.W.J, Dental materials and their selection, 3rd edition, Quintessence publications.
Craig.R.G, Dental Materials, 12th edition, Elsevier publications.
Anusavice, Phillip’s Science of Dental Materials, 11th edition, Saunders publications. Impression materials.
References